It is often practically important to mix a finely divided dry solid material into a liquid and/or a slurry of solids in liquid, the phrase “liquid and/or a slurry of solids in liquid” and its optionally plural form “liquid(s) and/or at least one slurry of solids in liquid(s)” both being sometimes abbreviated hereinafter as “LSSL.” When such mixing must be done while a gas such as air is moving laterally with respect to upper surface of the LSSL, as when working outdoors with natural winds blowing, some of the finely divided solid can be entrained by the moving gas, thereby preventing it from reaching the surface of the LSSL into which it is intended to be mixed and instead depositing it eventually as an unwanted dust in some other place. This phenomenon is called “dusting” in this specification.
Many attempts to avoid this problem have been described in prior art, but none has been found to be fully satisfactory for both effectiveness of dust reduction and economy of operation in every situation. In particular, objectionable dusting has been observed on some windy days when using earth moving machinery such as bulldozers and hydraulic excavators (hydraulic excavators being more commonly called “track hoes” or “trackhoes”) to mix finely divided pozzolanic solids, and optionally other finely divided solids, into the slurries found in large oilfield pits containing previously used drilling mud and cuttings, as described in detail in U.S. patent application Ser. No. 10/037,630, filed Jan. 3, 2002, the entirety of the specification of which, except for any part thereof that may be inconsistent with any explicit statement herein, is hereby incorporated into this specification by reference.
Accordingly, a general object of this invention is to provide a mixer and mixing process that is less prone to unwanted dusting when mixing a finely divided solid material into a LSSL under conditions when there is lateral motion of a gas above the surface of the LSSL into which the finely divided solid is desired to be mixed. More particularly, a mixer and mixing process less dusting-prone than using earth moving equipment is provided for mixing finely divided pozzolanic and/or solids that reduce the plasticity index, i.e., the numerical difference between the plastic limit and the liquid limit, of the LSSL into slurries contained in oilfield pits in which used drilling mud and cuttings have been stored. (Materials that reduce the plasticity index of the LSSL when mixed with the LSSL are hereinafter usually denoted briefly as “plasticity-reducing materials.” Most pozzolanic materials are also plasticity-reducing materials for slurries of most soils and/or drilling cuttings in liquids.) Most preferably the mixer and mixing process provided are capable of adequately mixing a finely divided pozzolanic and/or plasticity-reducing solid material with the contents of a large pit at least as rapidly as the use of earth moving machinery and at no greater overall cost.